Environment sensors for measuring the temperature and humidity have been conventionally put into practical use. These environment sensors are widely used in, e.g., food processors such as microwave ovens, household electric products such as air-conditioners, business machines such as copying machines, cooling water temperature monitors of automobiles, various types of air-conditioners, and weather observation.
Generally, an environment sensor individually measures the temperature and humidity. Japanese Patent Laid-Open No. 2002-90329 proposes a capacitance humidity sensor. However, the relative humidity changes with temperature even for the same water content. Japanese Patent Laid-Open No. 6-242048 proposes a heat conduction type humidity sensor which performs compensation by temperature. Also, Japanese Patent Laid-Open No. 5-149901 proposes a humidity sensor obtained by forming two temperature-sensitive elements in parallel on the same substrate.
In temperature and humidity measurements, necessary specifications depend on applications. For example, in houses and offices, to keep comfortable living environments by finely controlling the operating conditions of, e.g., air-conditioners, the humidity and temperature distributions in living spaces must be measured. Food processors such as microwave ovens require a small-sized environment sensor capable of high-speed response in order to efficiently perform a variety of cooking. Furthermore, to perform optimal image formation in business machines such as copying machines, measurements of the temperature and humidity of printing sheets which change from moment to moment must be performed at higher speed in more detail than when performed by the conventional sensors. Also, in the fabrication processes of various IC circuits and the like, the environmental factors such as the temperature and humidity are required to be measured at higher accuracy than those of the conventional sensors.
Conventionally, the temperature and humidity are separately measured by a temperature measurement sensor and humidity measurement sensor. This increases the environment sensor scale, and prevents downsizing of sensors. In addition, the response speed is low in humidity measurement. Accordingly, the conventional humidity sensor cannot be used to set printing conditions when high-speed printing is to be performed by a copying machine or the like.
Also, with the spread of the Internet, information in a remote place is often processed by a server. This increases the necessity to transmit signals from environment sensors by radio.